Hi,
Although I can't relate to your situation as such, I can relate to threatening to split up all the way through a relationship. I have been married for nearly 8 years and I hate it but I constantly threaten divorce or leaving him. I hate that in myself. And of course if he ever left me, I would feel like the victim.
Your situation does sound very unhealthy for you and I just hope you have the strength to move on and leave this person for good. But I also understand how hard it is when you crave that closeness and connection with someone. I wish you luck with making the right decision